Scala Notes

 

Builder Pattern (Scala, Java) SparkSession uses builder patterns

https://www.freecodecamp.org/news/how-to-solve-the-builder-patterns-boilerplate-problem-2ea97001dbe6/ 

The builder pattern is great for classes that can have complex initialization. It typically consists of setting values for multiple variables, some of which may be required with the rest being optional. 
…in which you provide a constructor with only the required parameters, another with a single optional parameter, a third with two optional parameters, and so on, culminating in a constructor with all the optional parameters.

Actually writing a builder can be quite a tedious and repetitive task.

Doing it dynamically - using Lombok library - which does dynamic code generation

@Builder annotation - if applied on a class (POJO) will create its Builder class automatically

Support @Builder on Person class will create PersonBuilder class ad you can set it as below

Person.builder().firstName("Adam").lastName("Savage") .city("San Francisco").jobTitle("TV Personality").build(); 

Tail-Recursion (import scala.annotation.tailrec)

All recursive cases are not tail-recursive (factorial is not, becuase it has to

keep intermediate result - but GCD is - because it does not have to memorize)

https://www.geeksforgeeks.org/tail-recursion-in-scala/

https://www.scala-exercises.org/scala_tutorial/tail_recursion

Example: GCD aka GCF https://www.khanacademy.org/math/cc-sixth-grade-math/cc-6th-factors-and-multiples/cc-6th-gcf/v/greatest-common-divisor

 Monad

Closures

Trait

List manipulation

var myList = List.empty[String]

 myList :+= "sree"

myList

res2: List[String] = List(sree)

Immutable by design - helps with concurrent programming

Option - 

Yield -  produces a value for each iteration

Null, Nil, None, Nothing

Null - absense of value

Nil - end of list

 None - value of an Option which has no value in it

Nothing - lowest type in the entire type system (Method which throws exception returns Nothing as the return type; all values under val, var falls under this)

Extractor Object - with unapply method (match the value and take it apart)

Pattern matching - case statement

def matchValue(x: Int): String = x match {

          case 1 => "One"

          case 2 => "Two"

          case _ => "many" 

            }

 Queue  val emptyQ = new scala.collection.mutable.Queue[Int]